Patent GB-637393-A (GB)
Title: Improvements in or relating to electrical circuit breakers and electrical circuit protection systems
IPC: H01H33/28
Filed: 1947-07-18
Abstract: 637,393. Electromagnetic switches; airbreak switches. FORMAN. J. July 18, 1947, No. 19347. [Class 38 (v)] A switch comprises means for normally maintaining it closed and means for opening or tripping it, the latter comprising a non- ferromagnetic repulsion member of good electrical conductivity, a repulsion coil adjacent said member, a storage system for electrical energy and means for discharging the system through the coil in a current pulse so as to produce repulsion between the coil and the member to open the switch. The contacts 1, 2, Fig. 2, are normally held closed by compressed air, admitted through a non-return valve V and acting on a copper or aluminium disc 10 secured to a tube 3 connected to contacts 2 through a rubber cushion 17. Upon energization of the coil 11 by a current pulse, the disc 10 is repelled upwards with the contacts 2, and a second repulsion member 18 moves downwards to compress air in the contact chamber to minimize risk of arcing. The air pressure on disc 10 is released through ports 20 in a sleeve 19 movable therewith. When the ports 20 pass ports 24 in the case 15 the pressure builds up again and the disc is retarded until ports 20a and 24 release the pressure again. The contacts are reclosed by manually moving the rod 25 downwards. In a modification, Fig. 4, the contacts are held closed by a coil 4 energized over contacts 6a, which are opened upon energization of coil 11 by downward repulsion of a ring member 8. Upward movement of disc 10 is initially unrestricted due to a lost-motion connection between tube 3 and contact 2 and is finally retarded by a coil 13. The contacts are held open by the coil 4 acting on a second armature 6b on tube 3, the coil 4 being re-energized at the end of the said current pulse. A spring 5 absorbs the recoil of the coil 11. In a further modification (Fig. 1, not shown), the contacts are held open by a mechanical latch and a further coil is provided to stop the disc 10. Protective cut-out arrangements.-Upon a fault in the line 26, the voltage induced in a coil 36, acting as the secondary of a saturable reactor 37, breaks down an intermediate sparkgap 32, 31, to trigger the main gap 31, 31, thereby discharging a condenser 30 through the coil 11 to operate a switch, as in Specification 605,747, [Group XXXVI]. At the same time a pulse is applied over transformer 33 to fire a thyratron 42 and so discharge a condenser 43 through the retarding coil 13, a second pulse being applied in the reverse direction through a second gas-filled valve 46 and the stopping coil 14. The switch is reclosed by means of a manual switch 50 energizing the coil 14 by means of an impulse from a condenser 47, the switch 50 also automatically tripping the mechanical latch (when provided) or momentarily de-energizing the coil 4 when this is arranged to hold the contacts 2 open, as in Fig. 4. Arc-rupturing in switches.-In addition to the member 18 in Fig. 2, the switch is arranged to open at the zero of the cycle by a phase adjuster 40, Fig. 3, controlling the moment of sparking at 32, 31. Further, a reverse current impulse is applied to the contacts 1, 2, from a condenser 52 which is discharged over valves 55, 56 when these strike. upon increase of voltage in the winding 67 of reactor 37, the impulse being such as to neutralize the voltagerise at the contacts 1, 2 during opening. Specification 637,392 also is referred to.